The present invention relates to lasers and in particular to lasers capable of providing multiple discrete output colors switched in time (time division multiplexing).
Many important applications for lasers require multiple and specific wavelengths. For example, U.S. Pat. No. 5,912,178 entitled: “Passive Measurement of Isotopes to Monitor Health”, assigned to the assignee of the present invention and hereby incorporated by reference, describes a system for monitoring the ratio of C12 to C13 in a patient's breath to establish the health of the patient. In this application, a first laser may provide a beam having a wavelength aligned with a C12O162 feature and a second laser may provide a beam having a wavelength aligned with the C13O162 feature. In addition, a third laser may provide a beam having an intermediate wavelength with negligible absorption by CO2 as a baseline reference.
In order to detect absorption of the laser light separately for each of these features, multiple optical paths and detectors may be used, or the different colors may be separated optically using filters or the like. The need for multiple lasers and associated optical components increases the cost and size of such systems.
Co-pending U.S. application Ser. No. 11/749,553, filed on May 16, 2007, assigned to the same assignee as the present invention, and hereby incorporated by reference, describes a laser that may produce multiple discrete output colors using a laser cavity having a different effective optical length at the different colors. The desired colors are selected by pulsing (switching on) an optical amplifier at multiple different boost frequencies to boost only those cavity modes compatible with the desired colors. This “mode locking” process allows the generation of two or more, narrow linewidth, predetermined output colors, each modulated by the different boost frequencies applied to the optical amplifiers. This modulation allows the different colors to be distinguished not only by frequency of the light but also by the frequency of their modulation.